1. Technical Field of the Invention
The present invention relates to a mold clamping device for an injection molding machine with at least one injection mold wherein a first injection mold half is supported by a first stationary mold plate and a second injection mold half is displaceable via a mold carrier that can be moved on at least two tie bars between the first stationary plate and a second stationary plate by means of at least a long-stroke drive cylinder-piston unit for rapid opening and closing of the injection mold halves, and the respective injection mold halves are closeable under high pressure by means of a short-stroke pressure pad device. Coupling bolts are provided that can be moved radially with respect to the longitudinal axis of the press plunger of the pressure pad device.
2. Discussion of the Related Art
Devices for moving a highly loadable punch in succession are known and include, for example, a clamping unit for plastic injection molding machines or a hydraulic press which enable the punch to move over a segment of its path at a high speed with low feeding power or at a low speed with high feeding power. To drive the punches of hydraulic presses, stepped pistons have often been used whose entire stroke is subdivided between a feed in rapid traverse by loading only the small piston surface or with a slower feed, and an increased press force out upon loading the entire piston surface. To actuate the clamping unit for plastic injection molding machines, elbow lever drives are velocity, the elbow lever is automatically driven and brings about a significant increase in the clamping force acting on the punch with the approach of the elbow levers at the extended position. The major drawbacks of such an elbow drive for the punches are that the final position of the tool carrying surface must be accurately adjusted for each mold and the punch stroke for a design-defined length of the elbow levers can be changed only within a very limited range.
To simplify this device, it has been proposed in West German patent application DE-OS 17 29 314 to provide, in addition to hydraulic working cylinders with a large stroke and small cross section for the rapid power traverse of the punch in the working and return direction, a support rod that is connected to a punch via another hydraulic working cylinder having a large cross section and small stroke and that is guided in a fixed abutment during rapid power traverse. Just before setting the punch, starting from which an increase in the feeding power is necessary to close the injection mold, the locking device, which was open up to this instant to enable a powerless comovement of the support rod for the punch, is closed between the support rod and the fixed abutment. Immediately thereafter, the working cylinder between the support rod and the punch having a large piston cross section is loaded with pressure fluid so that on its terminal path portion, which constitutes a very short fraction of its total path, the punch is moved into its end position with a significantly increased feeding power and at a correspondingly reduced velocity. As an embodiment for the locking device, at least two jaws that can be moved at the abutment in the radial direction with respect to the support rod are disclosed. These jaws interact with preferably several grooves that are uniformly spaced on the support rod and extend at right angles to the longitudinal direction of the support rod. A drawback of this device lies in the long reversing periods for the pressure medium.
In the West German patent application DE-AS 20 20 88, a mold clamping device of this type is described in which a pressure spindle, which can be moved into a bore of the press plunger, is attached to the movable mold carrier in order to transfer power. To couple the power mechanically between the squeezing stroke piston and the pressure spindle, two pressure ring halves are moved into position so that their cone-shaped face abuts against a correspondingly designed truncated cone-shaped contact surface at the face side of the pressure spindle. In this manner power essure spindle.
It has also already been proposed to clamp together the mold platens directly via the locking tie bars. To this end there are four hollow-bored lacing tie bars in whose bores extend auxiliary pistons for the closing and opening movement. As soon as the tie bars are moved into position and the mold is moved into the closed position, a mechanical locking that mates in the ring-shaped grooves of the tie bars is hydraulically actuated. The locking elements acting at this stage as pistons are hydraulically loaded with high pressure via intermediate rings acting as pressure pads and clamp the tie bars with the generation of the mold locking force.
In West German patent application DE-OS 21 02 725, in order to minimize the technical complexity it is proposed to provide the respective locking device with locking wedge surfaces which can be locked with a clamping pressure that simultaneously generates the closing and locking force in one working step with the locking mechanism. This method has the advantage that the locking tie bars can be solid. They are provided with a thread by means of which they can be adjusted longitudinally with respect to their mold platen via the tightening nuts. On their free end the locking tie bars have ring-shaped grooves which interact with the locking devices of the stationary mold platen, e.g., wedges. In this example, the locking device would have locking wedge surfaces which can be locked with the clamping pressure that simultaneously generates the closing and locking force in one working with the locking mechanism. Of course, the clamping forces that are hereby generated are relatively low.
West German patent application DE-OS 34 34 863 discloses a closing mechanism of an injection molding machine having a hydraulically driven cylinder-piston unit, which performs two substrokes of which the first is traversed faster than the second. A displacement pipe projects axially into the cylinder chamber and the piston, is attached to one face wall of the cylinder, and is open on the driven-out end of the displacement area. To keep the flow cross section for the post-suction lines small and to be able to omit an oil tank above the cylinder, it is proposed that the piston, whose stroke remains constant regardless of the height of the injection mold, actuate an elbow lever mechanism, and that the maximum overlapping length of the displacement area of the displacement pipe with the piston corresponds to the first substroke of the piston. The displacement pipe is then attached to a suction valve of an oil tank or the like.
In addition, West German patent application DE-OS 37 15 160 discloses that the closing force to be generated and corresponding to the selected cavity pressure is generated by means of an electromagnet, which exerts a mold-oriented force on the ram in a current-driven state.
Accordingly, it is an object of the present invention to simplify the design of the aforementioned mold locking device.
It is another object of the present invention to improve the aforementioned mold locking device such that the cycle periods of the molding sequences and the energies expended in closing and opening the injection mold halves are minimized.
Additional objects and advantages of the present invention are apparent from the specification and drawings which follow.